Numerous cryogenic distillation processes for the production of nitrogen are known in the art, among these are the following:
U.S. Pat. No. 3,217,502 discloses a process in which feed air is introduced at a higher pressure than is usual for nitrogen generators and in which, after the recovery of nitrogen, the entire quantity of oxygen rich air is expanded to produce the necessary refrigeration for the process. The patent further discloses that by the use of reversing heat exchangers and a multiple pressure fractionator, a high purity, high pressure nitrogen product is available without further compression or other refrigeration sources.
U.S. Pat. No. 3,492,828 discloses a process for the low temperature separation of a raw gas mixture containing one higher boiling component. In the process, the required refrigeration is produced in a refrigeration cycle and the higher boiling component is condensed during cooling of the raw gas and is subsequently removed from the plant together with the impure separation product to be warmed. Heat exchange in the process is carried out between the raw gas and the separation product and in the refrigeration cycle, between the compressed cycle gas and the expanded cycle gas in at least one plate-fin heat exchanger.
U.S. Pat. No. 3,735,599 discloses an air separation apparatus which comprises a reversing heat exchanger, an air liquefier, a single column rectifier provided with a condenser-evaporator and a cold generation device. In this apparatus, air is cooled in the reversing heat exchanger and liquefied in the air liquefier, the liquefied air is rectified in the single column rectifier to separate into liquid air abundantly containing oxygen and highly pure nitrogen gas. The liquid air is subjected to heat exchange in the condenser-evaporator. The resulting gasified air is subjected to heat exchange in the air liquefier and sent through the reversing heat exchanger to the cold generation device. The resultant liquefied air is sent through the air liquefier and the reversing heat exchanger to release. The patent also discloses a process for controlling the separation of cold which is characterized in that a by-pass channel is provided for communicating a position on a passage between the condenser-evaporator and the air liquefier and a position on a passage between the cold generation device and the air liquefier. A control valve is provided on the by-pass channel and the opening degree of the control valve is automatically controlled so as to regulate appropriately the flow volume of the gaseous air passing through the by-pass channel whereby the level of the liquid air in the condenser-evaporator is kept constant and the rectification of the liquefied air in the single column rectifier is carried out under stable conditions.
U.S. Pat. No. 3,736,762 discloses a method of producing gaseous and liquefied nitrogen having a pressure higher than atmospheric pressure, by the use of an apparatus comprising a reversible heat exchanger and a single column rectifier. In the process, impure gas obtained by heat-exchanging, in a condenser-evaporator, of liquefied air with nitrogen gas, each of which has been separated in the column, is divided into two parts. One of these parts is again divided into two parts; one part of this second division is passed through a control valve and then through the heat exchanger, after which it is united and admixed with the remaining part of the gas resulting from the second division, which has passed through a control valve. This admixture is supplied to an expansion turbine; the expanded impure gas is united and admixed with the remaining part of the gas resulting from the original division, which has passed through a control valve. This admixture, after having been passed through the air-liquefier and then the heat exchanger, is removed from the apparatus.
U.S. Pat. No. 4,222,756 discloses a process for producing nitrogen which comprises removing all or substantially all carbon dioxide and water vapor from air and introducing said air at between 85 and 125 psia and below -260.degree. F., into a first distillation column. At least part of the overhead product from said first distillation column is expanded in an expander to a pressure in the range of 45 to 70 psia and at least part of the bottoms product from said first distillation column is expanded to a pressure in the range 45 to 70 psia. At least part of both expanded products are introduced into a second distillation column. A part of the refrigeration contained in the bottoms product of said second distillation column is used to provide reflux in said first distillation column. At least a part of the bottoms product from said second distillation column is expanded to a pressure equal to or less than 30 psia. A part of the refrigeration therein is used to provide reflux in said second distillation column. Nitrogen product is removed from the top of said second distillation column. The patent also discloses an apparatus for carrying out the process.
U.S. Pat. No. 4,530,708 discloses an air separation method and apparatus for liquefying and separating feed air into oxygen and nitrogen by use of a single rectification column. The temperature of the feed air, which is liquefied, is reduced to the temperature necessary for the condensation and liquefaction of pure vaporous nitrogen inside the single rectification column and is used to condense and liquefy the pure vaporous nitrogen and vaporize the feed air. After the pressure of the feed air thus vaporized is raised to the pressure necessary for the condensation and liquefaction of the pure vaporous nitrogen inside the single rectification column, the vaporized feed air is introduced into the single rectification column so that pure gaseous nitrogen can be withdrawn from the top of the single rectification column, pure gaseous oxygen from a lower portion of the column and waste gas rich in nitrogen from an intermediate portion of the column. Thus, the present invention makes it possible to carry out air separation with a high rate of recovery of oxygen using a single rectification column.